1. Field of the Invention
The present invention relates to a vertebral osteosynthesis equipment.
2. Description of the Related Art
A vertebral osteosynthesis equipment generally includes bony anchoring members, such as pedicular screws or hooks, one or two linking rods, intended to be connected to these anchoring members and to be attached to the vertebrae by dint thereof, and parts for connecting this(these) linking rod(s) to these anchoring members. The equipment may also comprise length-adjustable crossbeams, which link transversally two parallel linking rods in order to hold said rods with respect to one another.
In an existing type of equipment, each anchoring member comprises a proximal threaded stud whereon a nut may be screwed, and each connecting part comprises a rounded section intended for surrounding a linking rod and two parallel branches drilled with holes. These branches are intended for engaging onto said proximal stud and for being clamped, by means of that nut, against a bearing surface provided on the anchoring member, said operation enabling to clamp said rounded section around the linking rod and thereby ensuring longitudinal immobilisation of this rod with respect to the anchoring member. The anchoring members may be of “monoaxial” type, i.e. comprise a proximal threaded stud integral with the base portion of the anchoring member serving for bony anchoring, or may be of “polyaxial” type, i.e. comprise a proximal threaded stud articulated with respect to that base portion.
When installing the equipment, the anchoring member(s) are placed on the vertebrae, then extension pieces are engaged on the proximal studs of these anchoring members. The connecting parts, with the rod(s) engaged in their rounded portions, are then engaged on these extension pieces and run down along the latter until they rest on the anchoring members. The extension pieces are then withdrawn and the clamping nuts are placed.
To enable adequate correction of the position of the vertebrae, the linking rod(s) must be shaped in one or several planes. This operation leads to successive trials until the adequate form is obtained. Successive insertions and retractions of the extension pieces and successive running down operations of the assemblies composed of connecting parts—linking rods along the latter, then withdrawing the extension pieces for placing the nuts, are then relatively tedious and time-consuming operations.
Moreover, with polyaxial anchoring members, the movements of the proximal studs modify the positions of the connecting parts and disturb consequently the determination of the form which should be given to the linking rod(s) so that these rods may be engaged in these connecting parts, which disturbs noticeably the installation of the equipment.
It is besides known by the documents US 2003/028191 or U.S. Pat. No. 6,050,997 to provide a single-branch connecting part, with a closed housing for receiving the linking rod, fitted with a screw, this screw enabling to clamp the linking rod in this housing.
This connecting part structure is assessed as non-optimal, from the handiness viewpoint of the equipment at installation as from the viewpoint of the clamping obtained.